Spring Boot - 环境@Autowired 抛出 NullPointerException [英] Spring Boot - Environment @Autowired throws NullPointerException

问题描述

我有一个使用 Spring Boot 0.5.0.M5 的项目设置.

I have a project setup using Spring Boot 0.5.0.M5.

在其中一个配置文件中，我尝试 @Autowire Environment 但失败并显示 NullPointerException.

In one of the configuration files I am trying to @Autowire Environment but that fails with a NullPointerException.

这是我目前所拥有的:

Application.java

@EnableAutoConfiguration
@Configuration
@ComponentScan
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

JpaConfig.java 我正在尝试 @Autowire Environment

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(basePackages = "com.ui.persistence.repository")
public class JpaConfig {
    private static final String DATABASE_DRIVER = "db.driver";
    private static final String DATABASE_PASSWORD = "db.password";
    private static final String DATABASE_URL = "db.url";
    private static final String DATABASE_USERNAME = "db.username";
    private static final String HIBERNATE_DIALECT = "hibernate.dialect";
    private static final String HIBERNATE_SHOW_SQL = "hibernate.show_sql";
    private static final String ENTITYMANAGER_PACKAGES_TO_SCAN 
        = "entitymanager.packages.to.scan";

    @Autowired
    private Environment env;

    @Bean
    public DataSource dataSource() {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName(env.getProperty(DATABASE_DRIVER));
        dataSource.setUrl(env.getProperty(DATABASE_URL));
        dataSource.setUsername(env.getProperty(DATABASE_USERNAME));
        dataSource.setPassword(env.getProperty(DATABASE_PASSWORD));
        return dataSource;
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
        LocalContainerEntityManagerFactoryBean entityManagerFactoryBean 
                = new LocalContainerEntityManagerFactoryBean();
        entityManagerFactoryBean.setDataSource(dataSource());
        entityManagerFactoryBean.setPersistenceProviderClass(
                HibernatePersistence.class);
        entityManagerFactoryBean.setPackagesToScan(
                env.getProperty(ENTITYMANAGER_PACKAGES_TO_SCAN));
        entityManagerFactoryBean.setJpaProperties(hibernateProperties());
        return entityManagerFactoryBean;
    }
}

我正在尝试加载在属性文件中配置的数据库属性.但是，Environment 没有注入，代码失败并显示 NullPointerException.我在 XML 文件中没有任何配置.

I am trying to load the database properties configured in a properties file. However, the Environment is not injected and the code fails with NullPointerException. I do not have any configuration in XML files.

对于属性文件，我以这种方式配置了PropertySourcesPlaceholderConfigurer:

For the properties file I have configured PropertySourcesPlaceholderConfigurer this way:

@Configuration
@PropertySource("classpath:database.properties")
public class PropertyConfig {
    @Bean
    public static PropertySourcesPlaceholderConfigurer propertyPlaceHolderConfigurer() {
        return new PropertySourcesPlaceholderConfigurer();
    }
}

我尝试过交换 @Autowired、@Resource 和 @Inject 但到目前为止没有任何效果.将不胜感激任何帮助.谢谢.

I have tried swapping @Autowired, @Resource and @Inject but nothing has worked so far. Would appreciate any help. Thanks.

推荐答案

我相信 Spring 和 EntityManagerFactory 存在一些生命周期问题，您可能已经遇到了这些问题(在 4.0.0 中修复).0.RC1) - 如果您的 @Configuration 类超早实例化，它可能不符合自动装配的条件.如果是这种情况，您可能可以从日志输出中判断出来.

I believe there were some lifecycle issues with Spring and the EntityManagerFactory, and you might have fallen foul of those (fixed in 4.0.0.RC1) - if your @Configuration class gets instantiated super early, it might not be eligible for autowiring. You can probably tell from the log output if that is the case.

只是出于兴趣，您是否知道 JpaConfig 和 PropertyConfig 提供的功能如果您使用 @EnableAutoConfiguration (只要您 @ComponentScan 定义了您的存储库的那个包)?请参阅 JPA以 Spring Boot 中的示例为例.

Just out of interest, did you know that the functionality provided by your JpaConfig and PropertyConfig is already presetn out of the box if you use @EnableAutoConfiguration (as long as you @ComponentScan that package where your repositories are defined)? See the JPA sample in Spring Boot for an example.

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